Supercritical fluid extraction of the omega-3 rich oil contained in hake (Merluccius capensis-Merluccius paradoxus) by-products: Study of the influence of process parameters on the extraction yield and oil quality

The supercritical fluid extraction (SFE) of the omega-3 rich oil contained in by-products of the fish industry has been studied in this work. Specifically, the offcuts obtained from peeling hake (Merluccius capensis-Meriuccius paradoxus) to obtain hake fillets have been used as raw material. This raw material was grounded to different sizes and freeze-dried to different moisture contents. Extraction experiments were carried out at different pressure, flow rate and flow sense in order to study the influence of such process parameters on the extraction rate and oil quality. The influence of continuous or intermittent contact solvent-subtract was also evaluated. The extraction temperature was maintained at 40 degrees C in all cases in order to avoid thermal degradation of the polyunsaturated fatty acids contained in hake oil. The results obtained indicate that internal mass transfer controlled the rate of the process under the conditions studied in this work. The optimum extraction conditions were found to be 25 MPa, 10 kgCO(2)/h and upflow sense over freeze-dried and grounded hake. Under those conditions, more than 96% of the total oil contained in the raw material was extracted after 3 h. The oil extracted presented a high omega-3/omega-6 ratio (around 7) and a high EPA and DHA content (about 6% and 14%, respectively, of the total fatty acids contained in the hake by-product used in this work). Quality and stability of the hake oil were evaluated along 14 days of storage under different conditions. The acidity of hake oil obtained by SFE was high, but it was similar or even lower than the acidity of the oil obtained by conventional solvent extraction. Acidity suffered little further increment along storage. Hake oil was very prone to oxidative modification, enhanced by increasing temperature and light. The oil oxidation process is complex affecting the concentration of parameters related both with primary and secondary steps of oxidation and to sensory properties as smell and colour. (C) 2008 Elsevier B.V. All rights reserved.